1. Field of the Invention
Disclosed herein are emulsified compositions containing two reactive species that produce zero-leakoff and methods of making and using such compositions.
2. Description of the Related Art
Stimulation treatment of wells is a common practice to enhance the production from oil and gas producing wells or the injectivity of water injection wells. Several ways exist to execute these stimulation treatments and their definition depends on the way the treatments are executed or the fluid used therein. When relatively small volumes of acids are used to remove the damage surrounding the wellbore, the treatment is referred to as matrix stimulation treatment. Matrix stimulation treatment generally involves pumping fluids, usually acids with other additives, to the wellbore and squeezing the fluids inside the formation to a shallow penetration depth. Normally, these fluids are pumped at pressures below the parting pressure of formation rock called “reservoir fracture pressure”. These matrix stimulation treatment fluids may contain acid only in their simplest form, but normally are mixtures of sophisticated formulations of various acids and other fluids pumped at different stages composing often a preflush, main fluid and postflush, depending on the geometry of the well, the history of its operations with corresponding damage cause and the lithology of its rock.
In carbonaceous formations, the positional change in reservoir properties, often called heterogeneity of the rock, plays a significant role in the outcome of the treatment. The heterogeneity is detrimental in a sense that it causes uneven distribution of the fluids to different layers or sections of the well. It is known that the acid will invade the porous and more permeable layers and sections more than invading the less porous and tighter parts. Even more significant, it causes the porous and permeable parts to become more permeable causing more fluids to invade the same section. The efforts paid by experts in the art to cause the acid to divert from its normal direction and go to tighter and less permeable parts of the formation is known as acid diversion in a process known by uniform acid placement.
Typically, heterogeneity effect is often of less severity in the vertical wells because of their relatively smaller penetration through the formation. On the other hand, placement of these fluids in the horizontal well is hard and a challenging task. Several methods are employed to overcome this challenge. The most common method is the employment of the coiled tubing unit to place these fluids across the formation rock. The coiled tubing unit is pulled out from the wellbore while filling the space inside the wellbore with the stimulating fluids. Rental and use of these coiled tubing units are expensive. Pumping the acid from the neck of the well, wellhead, in a process called bullheading is less expensive and more convenient. However, there is no existing technique that enables pumping these fluids using this method with good diversion of the fluids. Generally when this type of pumping method is utilized, the fluids, especially acid in carbonate wells, tends to get consumed in the heal of the well resulting in that zone receiving the majority of the stimulation fluids and leaving other parts away from the heal without stimulation.
Another method of the stimulation treatment is fracturing. Fracturing utilizes treating pressures above the reservoir fracturing pressure. Fracturing is normally classified into two main types depending on the fluid used during the closure of the fracture. If acid is used during the closure of the fracture, the treatment is referred to as an acid fracturing stimulation treatment. The enhancement of the production after this treatment depends on the etched surface on the walls of the fracture that is leftover after the exposure to the acid. If, on the other hand, sand, or proppant are used to leave the fracture open, the treatment will be called proppant fracturing treatment or more often hydraulic fracturing treatment. Other types of fracturing treatments do exist and are generally referred to as frac and pack and water fracs.
Acid fracturing is normally done for carbonaceous rock because only this type of rock can be etched upon exposure to acids. The enhancement in the permeability in the fractured well depends to a large extent on the conductivity of the resulting fracture. Most significantly, it depends on the etching degree of the surface after exposure to the acid. Also, it depends on the acid penetration length. Normally, the acid does not reach the tip of the created fracture because of its high spending on the inlet of the fracture.
The ratio of the acid penetration length to that of the created fracture is called fracturing efficiency. It is known that the spending of the acid in the fracture is controlled by the leakoff of the acid through the walls of the fracture and is affected largely by the retardation ability of the acid.
A need exists for methods and compositions that can be used to divert acid to different sections in horizontal and vertical wells. There is also a need for improved compositions and methods of fracturing well that provide for zero leakoff, do not penetrate the formation, and only form a sealing layer on the face of the formation.